Hitherto, from aspects of environments and resources, low fuel consumption (low rolling resistance) is strongly desired from vehicle tires. Further, superior wet-skid resistance is required from the viewpoint of safety and superior wear resistance is required from the viewpoint of durability.
When the carbon black content of a rubber composition which is utilized for a tire is increased for improving wear resistance, the value of tan.delta. (70.degree. C. ) becomes large and rolling resistance is also increased. Therefore, it is well known to employ silica instead of carbon black.
In such a case, it is also well known that a silane coupling agent can be employed to give reinforcement by improving the bonding ability (reactivity) between the silica and rubber components of a rubber composition.
However, there is a problem that a silane coupling agent is expensive which makes the cost of the tire higher as the mixing amount is increased.
There is disclosed, for example, in JP-B-80503/1993 the technology wherein reinforcement is obtained by reacting an alkoxysilane which is an organic silicon compound, of the one or make ends of a polymer molecule of rubber compoments in a rubber composition to chemically bond the alkoxysilane with silica.
According to the prior technology described in the publication, although reinforcement of the resulting rubber composition can be improved, there arises a problem that it is necessary to add a silane coupling agent because the processability of the rubber composition is inferior in the not-vulcanized state. Further the publication is silent on compatibility between low rolling resistance and high wet-skid resistance.
Considering the above-mentioned facts, an object of the present invention is to obtain a rubber composition for a tire tread which is superior in processability and has both low rolling resistance and high wet-skid resistance by decreasing the mixing amount of the silane coupling agent.